app-node.js

var http_port = 3000;

var http = require('http');
var htutil = require('./htutil');

var server = http.createServer(function(req, res){
    htutil.loadParams(req, res, undefined);
    if (req.requrl.pathname === '/'){
        require('./home-node').get(req, res);
    }else if (req.requrl.pathname === '/square'){
        require('./square-node').get(req, res);
    }else if (req.requrl.pathname === '/factorial'){
        require('./factorial-node').get(req, res);
    }else if (req.requrl.pathname === '/fibonacci'){
        require('./fibo-node').get(req, res);
    }else if (req.requrl.pathname === '/mult'){
        require('./mult-node').get(req, res);
    }else{
        res.writeHead(404, {'Content-Type': 'text/plain'});
        res.end("bad URL" + req.url);
    }
});

server.listen(http_port);
console.log('listening to http://localhost:3000');

htutil.js

var url = require('url');
exports.loadParams = function(req, res, next){
    req.requrl = url.parse(req.url, true);
    req.a = (req.requrl.query.a && !isNaN(req.requrl.query.a))
        ? new Number(req.requrl.query.a)
        : NaN;
    req.b = (req.requrl.query.b && !isNaN(req.requrl.query.b))
        ? new Number(req.requrl.query.b)
        : NaN;
    if(next) next();
}

exports.navbar = function(){
    return ["<div class='navbar'>",
        "<p><a href='/'>home</a></p>",
        "<p><a href='/mult'>Multiplication</a></p>",
        "<p><a href='/square'>Square</a></p>",
        "<p><a href='/factorial'>Factorial</a></p>",
        "<p><a href='/fibonacci'>Fibonacci</a></p>",
        "</div>"].join('\n');
}

exports.page = function(title, navbar, content){
    return ["<html><head><title>{title}</title></head>",
        "<body><h1>{title}</h1>",
        "<table><tr>",
        "<td>{navbar}</td><td>{content}</td>",
        "</tr></table></body></html>"
        ].join('\n')
        .replace(new RegExp("{title}", "gm"), title)
        .replace("{navbar}", navbar)
        .replace("{content}", content);
}

home-node.js

var htutil = require('./htutil');

exports.get = function(req, res){
    res.writeHead(200, {'Content-Type': 'text/html'});
    res.end(htutil.page("Math Wizard", htutil.navbar(), "<p>Math Wizard</p>"));
}

square-node.js

var htutil = require('./htutil');
exports.get = function(req, res){
    res.writeHead(200, {'Content-Type': 'text/html'});
    var result = req.a * req.a;
    res.end(
        htutil.page("Square", htutil.navbar(), [
            (!isNaN(req.a) ?
                ("<p class='result'>{a} squared = {sq}</p>"
                    .replace("{a}", req.a)
                    .replace("{sq}", req.a * req.a))
                : ""),
            "<p>Enter numbers to see its square</p>",
            "<form name='square' action='/square' method='get'>",
            "A: <input type='text' name='a' /><br/>",
            "<input type='submit' value='Submit' />",
            "</form>"
        ].join('\n'))
    );
}

factorial-node.js

var htutil = require('./htutil');
var math = require('./math');

exports.get = function(req, res){
    res.writeHead(200, {'Content-Type': 'text/html'});
    res.end(
        htutil.page("Factorial", htutil.navbar(), [
            (!isNaN(req.a) ?
                ("<p class='result'>{a} factorial = {fact}</p>"
                    .replace("{a}", req.a)
                    .replace("{fact}", math.factorial(Math.floor(req.a))))
                : ""),
            "<p>Enter numbers to see its factorial</p>",
            "<form name='factorial' action='/factorial' method='get'>",
            "A: <input type='text' name='a' /><br/>",
            "<input type='submit' value='Submit' />",
            "</form>"
        ].join('\n'))
    );
}

mult-node.js

var htutil = require('./htutil');
exports.get = function(req, res){
    res.writeHead(200, {'Content-Type': 'text/html'});
    var result = req.a * req.b;
    res.end(
        htutil.page("Multiplication", htutil.navbar(), [
            (!isNaN(req.a) && !isNaN(req.b) ?
                ("<p class='result'>{a} * {b} = {result}</p>"
                    .replace("{a}", req.a)
                    .replace("{b}", req.b)
                    .replace("{result}", req.a * req.b))
                : ""),
            "<p>Enter numbers to mutiply</p>",
            "<form name='mult' action='/mult' method='get'>",
            "A: <input type='text' name='a' /><br/>",
            "B: <input type='text' name='b' /><br/>",
            "<input type='submit' value='Submit' />",
            "</form>"
        ].join('\n'))
    );
}

fibo-node.js

var htutil = require('./htutil');
var math = require('./math');

exports.get = function(req, res){
    res.writeHead(200, {'Content-Type': 'text/html'});
    res.end(
        htutil.page("Fibonacci", htutil.navbar(), [
            (!isNaN(req.a) ?
                ("<p class='result'>{a} fibonacci = {fibo}</p>"
                    .replace("{a}", Math.floor(req.a))
                    .replace("{fibo}", math.fibonacci(Math.floor(req.a))))
                : ""),
            "<p>Enter numbers to see its fibonacci</p>",
            "<form name='fibonacci' action='/fibonacci' method='get'>",
            "A: <input type='text' name='a' /><br/>",
            "<input type='submit' value='Submit' />",
            "</form>"
        ].join('\n'))
    );
}

fibo2-node.js

var htutil = require('./htutil');
var math = require('./math');

function sendResult(req, res, a, fiboval){
    res.writeHead(200, {'Content-Type': 'text/html'});
    res.end(
        htutil.page("Fibonacci", htutil.navbar(), [
            (!isNaN(fiboval) ?
                ("<p class='result'>{a} fibonacci = {fibo}</p>"
                    .replace("{a}", a)
                    .replace("{fibo}", fiboval))
                : ""),
            "<p>Enter numbers to see its fibonacci</p>",
            "<form name='fibonacci' action='/fibonacci' method='get'>",
            "A: <input type='text' name='a' /><br/>",
            "<input type='submit' value='Submit' />",
            "</form>"
        ].join('\n'))
    );
}

exports.get = function(req, res){
    if (!isNaN(req.a)){
        math.fibonacciAsync(Math.floor(req.a), function(val){
            sendResult(req, res, Math.floor(req.a) ,val);
        });
    }else {
        sendResult(req, res, NaN, NaN);
    }
}

math.js

var factorial = exports.factorial = function(n){
    if (n == 0)
        return 1;
    else
        return n * factorial(n-1);
}

var fibonacci = exports.fibonacci = function(n){
    if (n === 1)
        return 1;
    else if (n === 2)
        return 1;
    else
        return fibonacci(n-1) + fibonacci(n-2);
}

var fibonacciAsync = exports.fibonacciAsync = function(n, done){
    if (n ==1 || n == 2)
        done(1);
    else {
        process.nextTick(function(){
            fibonacciAsync(n-1, function(val1){
                process.nextTick(function(){
                    fibonacciAsync(n-2, function(val2){
                        done(val1 + val2);
                    });
                })
            });
        });
    }
}